Sodium copper titanate compositions containing a rare earth, yttrium or bismuth

ABSTRACT

This invention provides compositions of the formula Na 0.5 M 0.5 Cu 3 Ti 4 O 12  wherein M=La—Lu, Y, Bi or mixtures thereof. These compositions have high dielectric constant and low loss over a frequency range of from about 1 kHz to about 1 MHz.

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/328,758, filed on Oct. 12, 2001.

FIELD OF THE INVENTION

[0002] This invention relates to novel compositions of the formulaNa_(0.5)M_(0.5)Cu₃Ti₄O₁₂ wherein M is La—Lu, Y, Bi or mixtures thereof.

BACKGROUND OF THE INVENTION

[0003] The use of dielectric materials to increase capacitance is wellknown and long-used. Known capacitor dielectrics fall into twocategories. One category of dielectrics has a relativelytemperature-independent dielectric constant but the value of thedielectric constant is low, e.g. 5-10. Materials such as electricalporcelain and mica fall into this category. Another category ofdielectrics has a very high dielectric constant, e.g. 1000 or more, butthey are quite frequency dependent. An example is barium titanate(BaTiO₃).

[0004] Since the capacitance is proportional to the dielectric constant,high dielectric constant materials are desired. In order to performacceptably in electronic circuits, the dielectric must have a dielectricconstant that exhibits minimal frequency dependence. It is alsodesirable to have the loss or dissipation factor as small as possible.The materials of this invention meets those needs.

SUMMARY OF THE INVENTION

[0005] This invention provides compositions of the formulaNa_(0.5)M_(0.5)Cu₃Ti₄O₁₂ wherein M is La—Lu, Y, Bi or mixtures thereof.These compositions have high dielectric constant and low loss over afrequency range of from 1 kHz to 1 MHz and are especially useful incapacitors in electronic devices such as phase shifters, matchingnetworks, oscillators, filters, resonators, and antennas comprisinginterdigital and trilayer capacitors, coplanar waveguides andmicrostrips.

BRIEF DESCRIPTION OF THE DRAWING

[0006]FIG. 1 shows the variation of dielectric constant and loss factorfor the compositions of Examples 2, 4, 6 and 7.

DETAILED DESCRIPTION OF THE INVENTION

[0007] The compositions of this invention, Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂,wherein M is La—Lu, Y, Bi or mixtures thereof, have dielectricproperties that provide advantages in electronic devices requiring ahigh dielectric constant with minimal frequency dependence and low loss.“La—Lu” is defined as all the lanthanide (rare earth) elements withatomic numbers from 57 through 71.

[0008] The compositions of this invention can be synthesized by thefollowing procedure. Stoichiometric amounts of the starting materialsare thoroughly mixed. The starting materials M₂O₃ (M is La—Lu, Y, Bi ormixtures thereof), CuO, TiO₂ and Na₂CO₃ are preferred. The mixed powderof starting materials is calcined at about 900° C. for about 12 hours.The calcined powder is reground and pressed to about 12.7 mmdiameter/1-2 mm thick disks. The disks are sintered in air at about 950°C. for 24 hours. In both the calcining and sintering steps, the rate oftemperature increase is about 200° C./hour from room temperature (i.e.about 20-25° C.) to the calcining or sintering temperature. The rate oftemperature decrease is about 150° C./hour from the calcining orsintering temperature to room temperature.

[0009] All of the Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂ phases of this inventioncrystallize in a cubic perovskite-related Im3 structure.

[0010] Dielectric measurements can be carried out on the disk samples.The faces of the disk-shaped samples are polished with a fine-grit sandor emery paper. Silver paint electrodes are applied on the faces anddried at about 70-100° C. The capacitance and the dielectric lossmeasurements can be performed by the two-terminal method usingHewlett-Packard 4275A and 4284A LCR bridges at a temperature of about25° C. over a frequency range of from about 1 kHz to about 1 MHz. Thecapacitance (C) and the dissipation factor are read directly from thebridge. The dielectric constant (K) is calculated from the measuredcapacitance (C) in picofarads from the relationshipK=(100*C*t)/(8.854*A), where t is thickness of the disk shaped sample incm, A is the area of the electrode in cm², and * indicatesmultiplication

[0011] The advantageous effects of this invention are demonstrated by aseries of examples, as described below. The embodiments of the inventionon which the examples are based are illustrative only, and do not limitthe scope of the invention.

EXAMPLES 1-7

[0012] The compositions Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂ of Examples 1-7 whereinM is La, Sm, Gd, Dy, Yb, Bi and Y, respectively, were made using thefollowing procedure. For each Example, appropriate amounts of thestarting oxides Na₂CO₃, M₂O₃, CuO and TiO₂ were weighed according to thestoichiometric ratios and mixed thoroughly in an agate mortar. The gramamounts of the starting materials used are shown in Table 1. TABLE 1 Ex.Composition Na₂CO₃ M₂O₃ CuO TiO₂ 1 Na_(0.5)La_(0.5)Cu₃Ti₄O₁₂ 0.06470.1989 0.5828 0.7803 (La₂O₃) 2 Na_(0.5)Sm_(0.5)Cu₃Ti₄O₁₂ 0.0641 0.21100.5777 0.7736 (Sm₂O₃) 3 Na_(0.5)Gd_(0.5)Cu₃Ti₄O₁₂ 0.0638 0.2182 0.57470.7696 (Gd₂O₃) 4 Na_(0.5)Dy_(0.5)Cu₃Ti₄O₁₂ 0.0635 0.2237 0.5725 0.7665(Dy₂O₃) 5 Na_(0.5)Yb_(0.5)Cu₃Ti₄O₁₂ 0.0630 0.2345 0.5680 0.7605 (Yb₂O₃)6 Na_(0.5)Bi_(0.5)Cu₃Ti₄O₁₂ 0.0614 0.2700 0.5532 0.7407 (Bi₂O₃) 7Na_(0.5)Y_(0.5)Cu₃Ti₄O₁₂ 0.0672 0.1433 (Y₂O₃) 0.6059 0.8113

[0013] In each Example, the mixed powder was calcined at about 900° C.for 12 hours. The calcined powder was reground and pressed to 12.7 mmdiameter/1-2 mm thick disks. The disks were sintered in air at about950° C. for 24 hours. In both the calcining and sintering steps, thetemperature was increased from room temperature to the calcining orsintering temperature at a rate of about 200° C./hour, and thetemperature was decreased from the calcining or sintering temperature toroom temperature at a rate of about 150° C./hour.

[0014] X-ray powder diffraction patterns were recorded with a SiemensD5000 diffractometer. The data showed all samples crystallized in acubic perovskite-related Im3 structure. The measured lattice parametersare listed in Table 2. TABLE 2 Dielectric Dielectric Lattice ConstantLoss, tan □ Parameter (10⁵ Hz) @ 298 (10⁵ Hz) @ 298 Ex. Composition (nm)K K 1 Na_(0.5)La_(0.5)Cu₃Ti₄O₁₂ 0.7420 3560 0.074 (1) 2Na_(0.5)Sm_(0.5)Cu₃Ti₄O₁₂ 0.7395 2263 0.047 (1) 3Na_(0.5)Gd_(0.5)Cu₃Ti₄O₁₂ 0.7388 2645 0.054 (1) 4Na_(0.5)Dy_(0.5)Cu₃Ti₄O₁₂ 0.7379 2049 0.035 (1) 5Na_(0.5)Yb_(0.5)Cu₃Ti₄O₁₂ 0.7361 2048 0.059 (1) 6Na_(0.5)Bi_(0.5)Cu₃Ti₄O₁₂ 0.7412 2952 0.065 (1) 7Na_(0.5)Y_(0.5)Cu₃Ti₄O₁₂ 0.7385 2375 0.048 (1)

[0015] The disk samples were polished to produce flat uniform surfacesand electroded with silver paint. The painted samples were dried atabout 70-100° C. overnight. Capacitance and loss tangent measurementswere done at room temperature using a HP-4284A LCR meter over afrequency range of from 1 kHz to 1 MHz. Dielectric constant and lossdata measured at a temperature of about 25° C. (298 K) and a frequencyof about 10⁵ Hz are listed in Table 2. The dielectric constants are highand the loss factors are low. Variations of dielectric constant and lossfactor over a range of frequency from about 10³ Hz to about 10⁶ Hz forthe samples of Examples 2, 4, 6 and 7 are shown in FIG. 1. Thedielectric constants and loss factors have minimal frequency dependenceover 3 orders of magnitude change in frequency.

What is claimed is:
 1. A composition of the formulaNa_(0.5)M_(0.5)Cu₃Ti₄O₁₂, wherein M is La—Lu, Y, Bi or mixtures thereof.2. A composition of the formula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂, wherein M isLa—Lu.
 3. A composition of the formula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂, whereinM is Y.
 4. A composition of the formula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂,wherein M is Bi.
 5. The composition of claim 1, wherein M is La, Sm, Gd,Dy, Yb, Y or Bi.
 6. The composition of claim 1, wherein M is La.
 7. Thecomposition of claim 1, wherein M is Sm.
 8. The composition of claim 1,wherein M is Gd.
 9. The composition of claim 1, wherein M is Dy.
 10. Thecomposition of claim 1, wherein M is Yb.
 11. A method of providing adielectric comprising providing a composition of the formulaNa_(0.5)M_(0.5)Cu₃Ti₄O₁₂, wherein M is La—Lu, Y, Bi or mixtures thereofas the dielectric.
 12. The method of claim 11 wherein M is Y or Bi. 13.An electronic device containing a capacitor with a dielectric material,wherein said dielectric material is comprised of a composition of theformula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂, wherein M is La—Lu, Y, Bi or mixturesthereof.
 14. An electronic device containing a capacitor with adielectric material, wherein said dielectric material is comprised of acomposition of the formula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂, wherein M is La—Lu.15. The electronic device of claim 13, wherein said dielectric materialis comprised of a composition of the formula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂,wherein M is La, Sm, Gd, Dy, Yb, Y or Bi.
 16. The electronic device ofclaim 13, wherein said dielectric material is comprised of a compositionof the formula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂, wherein M is La.
 17. Theelectronic device of claim 13, wherein said dielectric material iscomprised of a composition of the formula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂,wherein M is Sm.
 18. The electronic device of claim 13, wherein saiddielectric material is comprised of a composition of the formulaNa_(0.5)M_(0.5)Cu₃Ti₄O₁₂, wherein M is Gd.
 19. The electronic device ofclaim 13, wherein said dielectric material is comprised of a compositionof the formula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂, wherein M is Dy.
 20. Theelectronic device of claim 13, wherein said dielectric material iscomprised of a composition of the formula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂,wherein M is Yb.
 21. The electronic device of claim 13, wherein saiddielectric material is comprised of a composition of the formulaNa_(0.5)M_(0.5)Cu₃Ti₄O₁₂, wherein M is Y.
 22. The electronic device ofclaim 13, wherein said dielectric material is comprised of a compositionof the formula Na_(0.5)M_(0.5)Cu₃Ti₄O₁₂, wherein M is Bi.